This invention relates to a method and apparatus for severing thin strip material. More particularly, the invention relates to a method and apparatus for rapidly severing thin metal strip using a cutting element which rapidly moves transverse to the strip direction, such as a flying wire strip cutter.
In production of thin strip material, it becomes necessary to sever the strip in order to facilitate catching and coiling of the strip. For high-speed production processes, such as casting thin metal strip directly from the molten alloy to solid strip, such as is shown in U.S. Pat. No. 3,856,513, such strip is produced at speeds of between 2000 to 4000 feet per minute (610 to 1219 meters per minute). At such speeds, conventional methods and apparatus for severing the strip are not suitable.
For example, a conventional flying shear method where upper and lower shear blades are moved along the product with synchronized velocity, is not suitable. The distances necessary to accelerate the blades to the high-speed velocity and to decelerate after cutting are too great to make this a practical expedient. On the other hand, rotating shears which bring together rapidly rotating upper and lower units eliminate such distance requirements, such rotating shears, however, require complex and expensive equipment. Such a device also requires a threading feature to catch and thread the first or leading end of a strip through the unit.
Any such system which requires catching and threading of the leading end of a high-speed strip material has been found in the industry to be not practical for any system having vertically-moving upper and lower cutting units. In an effort to avoid such problems, U.S. Pat. No. 4,116,394, issued Sept. 26, 1978, discloses a device which uses a scissors-like action to catch and cut a thin strip material on a winding coil. However, such device is useful only once in a given operation as the strip is wound on top of it to build up the coil.
Even free-standing scissors-type cutting units might be useful if the blade action is quick enough to not act as a barrier which would substantially interfere with the strip movement. It appears that a blade dwell time of greater than 50 milliseconds would be unacceptable and because of such requirements, such a device has not been found acceptable.
A potential nonmechanical method using linear-shaped explosive charges can make cuts in about 1 millisecond or less using shock waves generated by the explosive charge. However, such devices are expensive, require particular skills in explosives, and require controlled stand-off distances commensurate with the explosive force in order to make the cut. Furthermore, shock waves appear to deflect ends of a severed strip from the path of travel and make recapturing of the new leading edge difficult.
What is needed is a method and apparatus for severing high-speed strip products quickly and in a low-cost manner without disrupting the production process. The method also should be useful over a wide range of gauge and product conditions.